This fly is about 1/2 inch (13 mm) in length and is characterized by an unusually large head in relation to the size of the insect, thus the name. It has mostly dark wings, and a long pedicel connecting the bulbous abdomen to the thorax. The eyes are black and the face is white. The thorax, abdomen and legs are also black except for a white band on the pedicel. The wings have a purplish-blue tint.
The frequency of occurrence is not known, but the individuals shown here were photographed at Neale Woods in mid-July and at Camp Brewster in late July.
This fly is distinguished from the other Thick-headed Fly in Nature Search by the Swollen hind thighs (tibia), and slightly thinner pedicel between the thorax and the abdomen. This family of flies is a parasite of solitary bees, and sometimes wasps. The female grabs the host while in flight and forces an egg between the bee’s abdominal segments. This genus includes 7 North American species.
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